You can spend a lot of accumulated time on your bottom in the course of a day. Or you can sit for lengthy spells without a break. Both, it turns out, are very bad for you.

Take a movement break every 30 minutes, say experts. No matter how much you exercise, sitting for excessively long periods of time is a risk factor for early death, a new study published Monday in the Annals of Internal Medicine found.

There's a direct relationship between time spent sitting and your risk of early mortality from any cause, researchers said, based on a study of nearly 8,000 Americans older than 45 who were asked to wear an accelerometer on their hip.

Over a period of 10 days, sitting or lounging behaviour took up the equivalent of 12.3 hours over a 16-hour waking day - about 77%, on average. That's a whole lot of sitting. But subjects differed in the extent to which they sat down for long stretches without getting up and moving around. When researchers measured the "bout length" of subjects' sitting spells, they found that 52% lasted less than a half-hour, 22% lasted between a half-hour and just under an hour, 14% lasted from one to one-and-a-half hours and 14% went on for more than that.

After tracking subjects for four years, the researchers found that subjects who recorded the most time sitting were most likely to have died during the study period, and those who spent the least time sitting were least likely to have died. That was no surprise.

As your total sitting time increases, so does your risk of an early death. The positive news: People who sat for less than 30 minutes at a time had the lowest risk of early death.

"Sit less, move more" is what the American Heart Association encourages all of us to do. But this simplistic guideline doesn't quite cut it, said Keith Diaz, lead author of the new study and an associate research scientist in the Columbia University Department of Medicine.

"This would be like telling someone just to 'exercise' without telling then how," Diaz wrote in an email.

Exercise guidelines are precise, he explained. For example, the US Centres for Disease Control and Prevention recommends adults do moderate-intensity aerobic exercise for two hours and 30 minutes every week, plus muscle strengthening activities on two or more days a week.

"We need similar guidelines for sitting," said Diaz. "We think a more specific guideline could read something like, 'For every 30 consecutive minutes of sitting, stand up and move/walk for five minutes at brisk pace to reduce the health risks from sitting,'" he said, adding the study "puts us a step closer to such guidelines, " but more research is needed to verify the findings.